Invasive ductal breast carcinomas comprise about 80% of all breast carcinomas and are characterized by the proliferation of tumor cells as well as an increase in fibrous tissue. There is growing evidence that fibroblasts found in proximity to the tumor cells also contribute to the malignant phenotype. The purpose of this application is to explore the interactions between these fibroblasts and the tumor cells which result in the expression of a particular metalloprotease, the 93 kDa type IV collagenase/gelatinase, also known as MMP-9. The family of metalloproteases contains several members whose expression has been correlated in vitro and in vivo with tumor progression, including invasion, metastasis, and angiogenesis. These enzymes degrade components of the extracellular matrix. Metalloproteases have been shown in some cases to be expressed in the tumor cells themselves, but in other cases, they are found in the stroma surrounding the tumor, normal stromal cells do not express these enzymes. MMP-9 has been shown to be required for metastasis in a sarcoma model system. Breast carcinomas contain MMP-9 mRNA. We have found that in a cell culture system, cocultivation of breast carcinoma cell lines with normal stomal cells can result in the induction of MMP-9. The goal of this proposal is to further study this induction. Since normal breast consists of many cell types including epithelial cells, fibroblasts, endothelial cells, and fat cells, we intend to determine which of these cell types can interact with the breast carcinoma cells to result in the induction of MMP-9, in which type of cell MMP-9 is expressed in these cocultures, and the level of regulation for this MMP-9 induction. Since both breast carcinoma cells and breast stromal cells may behave differently when exposed to estrogen and/or progesterone, we will determine whether either of these hormones influences MMP-9 induction. Finally, we will examine clinical specimens of breast carcinomas to correlate our in vitro findings with the localization of MMP-9 in vivo.